The present invention relates to an apparatus for inspecting ON-OFF states of a scattering-type liquid crystal display panel prior to mounting driving ICs (hereinafter referred to as "ON-OFF inspection apparatus"). More particularly, it relates to such ON-OFF inspection apparatus which is decreased in size by adopting direct viewing inspection.
The active-matrix drive liquid crystal display panel which uses a thin film transistor (hereinafter referred to as "TFT") as a switching element for each pixel comprises a TFT array substrate having a matrix array of TFTs, a counterpart substrate disposed in opposing relation the TFT substrate, and a liquid crystal material sealedly sandwiched between the two substrates. The TFT array substrate includes a glass substrate, scanning lines and data lines which are wired on the glass substrate as defining a matrix pattern, and a TFT serving as a switching element and a transparent electrode which are provided in each intersecting portion of the scanning lines and the data lines. The counterpart substrate includes a transparent electrode formed over the entire surface of the substrate, and a light-shielding film formed between each adjacent pair of pixels.
This liquid crystal display panel is composed of preparing the TFT array substrate and the counterpart substrate by respective thin film formation processes and patterning processes, disposing the two substrates in opposing relation to each other to define a predetermined gap therebetween, and introducing the liquid crystal material into the gap. Thereafter, an IC for driving TFTs is mounted on the liquid crystal display panel by TAB or COG method. Inspection takes place at each step until the product is completed. Among the inspections, the inspection on the liquid crystal display panel prior to the mounting of the IC is of great importance since it enables optical evaluation on the characteristics of the liquid crystal display panel itself. In addition, this inspection allows defective panels to be eliminated and, hence, only non-defective liquid crystal display panels are subjected to mounting of a driving IC. This leads to effective utilization of expensive driving ICs.
FIG. 26 is a schematic representation of a conventional ON-OFF inspection apparatus for a liquid crystal display panel just prior to the mounting of a driving IC. Liquid crystal display panel 101, prior to being subjected to the mounting of the driving IC, is fixed on a rigid body (not shown) with high precision. The scanning lines and data lines of the panel 101 respectively connect to the corresponding terminal electrodes (not shown) to be connected to the driving IC later while connecting to inspection terminal electrodes 102.sub.S1, 102.sub.S2, 102.sub.G1 and 102.sub.G2 disposed on four sides of the image display area. The suffixes S1, S2 and G1, G2 herein are meant to indicate electrodes for the data lines and those for the scanning lines, respectively. The terminal electrode 102.sub.S1 or 102.sub.S2 include terminals equal in number to the date lines. Likewise, the terminal electrode 102.sub.G1 or 102.sub.G2 include terminals equal in number to the scanning lines. Inspection probe pins 103.sub.S1, 103.sub.S2, 103.sub.G1 and 103.sub.G2 include pins equal in number and pitch to the terminal electrodes 102.sub.S1, 102.sub.S2, 102.sub.G1 and 102.sub.G2, respectively. Back light unit 104 includes a fluorescent lamp 105 and a diffusion plate 106. In the ON-OFF inspection on the liquid crystal display panel, the probe pins 103.sub.S1, 103.sub.S2, 103.sub.G1 and 103.sub.G2 are coming into contact with the inspection terminals 102.sub.S1, 102.sub.S2, 102.sub.G1 and 102.sub.G2, respectively, with high pecision. Signals are then input to the scanning lines and the data lines to cause the image display area to display a desired image, while the panel 101 is illuminated with diffused light emitted from the back light 104 disposed on the back side of the panel 101. The image thus formed is checked for a defect on a pixel or line basis either visually or by the use of a stereoscope or a TV camera.
The liquid crystal material for use in the liquid crystal display panel 101 is typically a twisted nematic (hereinafter referred to as "TN" simply) liquid crystal material, and the panel 101 is sandwiched by a pair of polarizers. In recent years, however, a light bulb of a projection-type LCD system has been employed a liquid crystal display panel of the type using a scattering-type liquid crystal material which assures a bright projected image since such light bulb dispenses with polarisers. In this liquid crystal display panel using the scattering-type liquid crystal material, pixels are ON-OFF controlled on the basis of the variation in transmission-scattering characteristics of the liquid crystal material against light. Therefore, the use of the aforementioned back light emitting diffused light renders the ON-OFF states of the image difficult to differentiate from each other, thus bringing a great difficulty in the ON-OFF inspection on the liquid crystal display panel.
To solve this problem, Japanese Unexamined Patent Publication No. 248435/1992 has proposed an LCD panel inspection apparatus as shown in FIG. 27. In this figure, there are shown a liquid crystal display panel 101, a projector 107, a reflecting mirror 108, a projection lens 109, a screen 110, a signal-generating circuit 111, and a drive-signal line 112. If the panel is an LCD panel using a scattering-type liquid crystal, polarlizers 113 are unnecessary. Light outgoing from the projector 107 is converged so that the beam diameter thereof at the opening of the projection lens 109 is substantially the same diameter of the opening of the projection lens 109.
Reference is then made to the operation of such an apparatus when used to inspect a liquid crystal display panel using a scattering-type liquid crystal. When the liquid crystal is in the transmissive condition, light outgoing from the projector 107 is reflected toward the projection lens 109 by the reflecting mirror 108, is directly incident on the opening of the projection lens 109, and reaches the screen 110, thereby increasing the luminance of the screen 110. On the other hand, when the liquid crystal is in the scattering condition, light outgoing from the projector 107 is scattered by the liquid crystal and hence will not be incident on the opening of the projection lens 109 and will not reach the screen 110. This results in the screen of a relatively low luminace. In this way the difference between the transmissive and scattering conditions of the liquid crystal is visually recognized as the difference in the luminance of the screen.
The conventional ON-OFF inspection apparatus for a liquid crystal display panel prior to the mounting of a driving IC is thus constructed and hence is required to form a projection optical system for inspecting a liquid crystal display panel using a scattering-type liquid crystal. This results in the apparatus of immense dimension.
The present invention has been attained to overcome the problems associated with the prior art. It is, therefore, an object of the present invention to provide an apparatus for inspecting a scattering-type liquid crystal display panel which is minimized in size, enhances the visuality of a display image to be inspected, and facilitates ON-OFF inspection on the scattering-type liquid crystal display panel.